The invention relates to a WDM optical transmission system, and more particularly, to a WDM optical transmission system in which jitter compression is realized and an optical transceiver is commonly used in different transfer rates and different coding formats.
FIG. 1 shows a conventional WDM (Wavelength Division Multiplexing) optical transmission system. In this conventional WDM optical transmission system, the reference numerals 1 and 2 indicate WDM optical transmission apparatus, 3, 4, 3xe2x80x2 and 4xe2x80x2 indicate optional optical transmission apparatus, 5 and 6 indicate optical transceivers, 7 indicates an electrical to optical converter for wavelength xcex1, 8 indicates an optical to electrical converter for wavelength xcex2 , 9 indicates an optical to electrical converter for wavelength xcex1, 10 indicates an electrical to optical converter for wavelength xcex2 , 11 indicates an electrical to optical converter for wavelength xcex3, 12 indicates an optical to electrical converter for wavelength xcex4, 13 indicates an optical to electrical converter for wavelength xcex3, 14 indicates an electrical to optical converter for wavelength xcex4, 15 and 16 indicate optical multiplexers/demultiplexers.
The optical transceivers 5 and 6 include optical signal receiving units 5-1 and 6-1, optical signal supplying units 5-2 and 6-2, and retiming units 5-3 and 6-3, respectively, while the optical transmission apparatus 3, 4, 3xe2x80x2 and 4xe2x80x2 include electrical to optical converters 3-1, 4-1, 3xe2x80x2-1 and 4xe2x80x2-1 and optical to electrical converters 3-2, 4-2, 3xe2x80x2-2 and 4xe2x80x2-2, respectively.
In this WDM optical transmission system, an optical signal of wavelength xcex1 sent from the electrical to optical converter 3-1 of the optical transmission apparatus 3 is received by the optical signal receiving unit 5-1 of the optical transceiver 5 of the WDM optical transmission apparatus 1. The optical signal is converted into an electrical signal by the optical signal receiving unit 5-1 and outputted to the retiming unit 5-3, by which the pulse width distortion generated between the optical transmission apparatus 3 and the WDM optical transmission apparatus 1 is corrected to effect jitter compression.
The electrical signal outputted from the retiming unit 5-3 is converted by the electrical to optical converter 7 into an optical signal of wavelength xcex1 and inputted to the optical multiplexers/demultiplexers 15. The optical signal is multiplexed with another optical signal of wavelength xcex3 outputted from the electrical to optical converter 11 to generate a WDM signal which is transmitted via an optical fiber 20 to the WDM optical transmission apparatus 2.
In this WDM optical transmission apparatus 2, the WDM signal inputted is demultiplexed by the optical multiplexers/demultiplexers 16 into optical signals of wavelength xcex1 and wavelength xcex3. The optical signal of wavelength xcex1 is converted into an electrical signal by the optical to electrical converter 9 and inputted to the optical transceiver 5. The electrical signal inputted to the optical transceiver 5 is converted into an optical signal by the optical signal supplying unit 5-2 and supplied to the optical transmission apparatus 3xe2x80x2, where the optical signal of wavelength xcex1 is converted into an electrical signal by the optical to electrical converter 3xe2x80x2-2.
Thus, communication from the optical transmission apparatus 3 to the optical transmission apparatus 3xe2x80x2 is performed. Communication from the optical transmission apparatus 3xe2x80x2 to the optical transmission apparatus 3 using an optical signal of wavelength xcex2, communication from the optical transmission apparatus 4 to the optical transmission apparatus 4xe2x80x2 using an optical signal of wavelength xcex3, and communication from the optical transmission apparatus 4xe2x80x2 to the optical transmission apparatus 4 using an optical signal of wavelength xcex4 are conducted in the same way.
In this WDM optical transmission system, optical transceivers 5 and 6 use a transfer rate and a coding format which are the same as those of the optical transmission apparatus 3, 4, 3xe2x80x2 and 4xe2x80x2. and the clocks are sampled in the retiming units 5-3 and 6-3 from the electrical signals generated by optical to electrical conversion, and the clocks are phase-synchronized with use of PLL (Phase Locked Loop) or narrow band filter, so that the pulse width distortion is corrected to effect jitter compression.
In the conventional WDM optical transmission system, however, there is a disadvantage in that the jitter generated in optical transmission between the WDM optical transmission apparatus 1 and 2 is transmitted without being corrected and is increased to deteriorate the quality of transmission signals, although jitter generated in optical transmission via the optical transceivers 5 and 6among the optical transmission apparatus 3, 4, 3xe2x80x2 and 4xe2x80x2 and may be compressed. Also, since the optical transceivers use the same transfer rate and coding format, respectively, as that used in each individual optical transmission apparatus, types of transceivers required increase.
Accordingly, it is an object of the invention to provide a WDM optical transmission system in which pulse width distortion generated in optical transmission between two WDM optical transmission apparatus is corrected so that jitter between them is compressed.
It is another object of this invention to provide a WDM optical transmission system comprising an optical transceiver which is used in common to various optical transmission apparatus having different transfer rates and coding formats.
According to the invention, a WDM optical transmission system performing communication in accordance with transmission and receipt of an optical wavelength division multiplexed (WDM) signal obtained by multiplexing optical signals of plural wavelengths having same or different transfer rates and coding formats, comprises:
a demultiplexer for demultiplexing a WDM signal to output the optical signals of plural wavelengths,
an optical to electrical converter for converting at least one of the optical signals of plural wavelengths into an electrical signal,
a retiming unit for correcting pulse width distortion of the electrical signal, and
an optical signal supplying unit for converting the electrical signal of which distortion of pulse width has been corrected into an optical signal to be outputted to an optical signal transmission medium.